The present invention relates to a metal cathode sheet assembly having an edge protector.
In the refinement of crude metals with the aid of electrolysis for extracting pure metal, metal is dissolved in an electrolysis tank from an impure anode and deposited in pure form on a cathode. Impurities remain dissolved in the electrolyte or form anode slime.
Various designs of electrolysis cathodes are seen among the related art. They differ mainly in the choice of materials or material combinations of the bearing rail and metal cathode sheet. The goal is to provide good electrical conductivity for minimizing energy losses, mechanical stability, and corrosion resistance.
In order to prevent the growing together of the metal layers deposited on both sides of the metal cathode sheet from reaching over the side edges, the side edges, which are vertically aligned in the electrolysis tank, are provided with an electrically insulating screen as edge protection.
In this connection, it is known to coat the side edges with wax. However, one disadvantage of using this method is that a large quantity of wax is required. Furthermore, if the wax is interspersed with contaminating particles, a bridge formation with the electrolyte can occur nonetheless, and can lead to an uncontrolled growth of metal buds. Such growth results in lower refining efficiency and can potentially disturbs the process sequence. Metal cathode sheets are therefore maintained in rotation, and the metal efflorescences are removed. This requires an operating interruption each time.
Among the related art there are solutions in which the side edges of the metal cathode sheets are provided with an edge protector of plastic.
In this connection, U.S. Pat. No. 5,919,343 describes a plastic shoulder as edge protector that is connected to the metal cathode sheet with the aid of plastic pins using fusion welding technology. Regardless, non-fused, faulty connection regions can be created, for example, by non-observance of constructive prerequisites with respect to the parts to be connected, by non-observance of certain welding parameters, and by errors in preassembly. Such faulty connections allow the passage of electrolyte and lead to uncontrolled formation of buds at the outer edge. The problem of local flux line concentration at sharp-edged borings in the metal cathode sheet, with its negative effects, has also not been solved.
Furthermore, U.S. Pat. No. 6,017,429 describes a metal cathode sheet having an electrically insulating edge protector made of plastic resistant to electrolyte. The edge profile is chemically connected to the metal cathode sheet, preferably using an adhesive or a vulcanizing technique. Again, the intimate combination of metal cathode sheet and edge profile is not absolutely ensured. Thus, with this embodiment, the infiltration by electrolyte under the wall of the edge profile can also take place.
In the metal cathode sheet known from U.S. Pat. No. 5,314,600, the edge protection is plastic rails that surround the vertical side edges of the metal cathode sheet in clamping fashion. On the side edges of the metal cathode sheet, bore holes are provided into which holding pins are fitted, by which the plastic rails are fixed. The edge protector is in loose combination with the metal cathode sheet. Thus, electrolyte can easily penetrate into the edge protector. Then, at the boring edges in the metal cathode sheet and at the inside sheet cutting edges, high local field densities can appear with the result that, particularly at these locations, uncontrolled metal growth takes place. After relatively longer-term application of the metal cathode sheet in the electrolyte, the plastic protector can be pried apart and damaged. This causes costly repair work or possibly a complete renewal of the edge protector.
It is an object of the present invention to create an improved metal cathode sheet for process applications which has an edge protector with relatively high mechanical stability and is advantageous from an application technology point of view.
Thus, in one embodiment of the invention, a metal cathode sheet assembly is provided for use in electrolytic recovery of pure metals. The assembly includes a cathode sheet having a side edge and at least one cutout through the side edge. The side edge having a narrow side. At least one trapezoidal holding wedge has back surfaces facing away from the narrow side. The holding wedge is secured to the at least one cutout, and is provided with a grooved profile. The edge protector is configured to engage the back surfaces of the holding wedge so that the edge protector is secured to the side edge of the cathode sheet.
In one embodiment of the invention, the edge protector is formed by a grooved profile strip that encapsulates the side edge. The edge protector is locked on the side edge using a fitting in of at least one trapezoid-shaped retaining wedge. For this purpose, the retaining wedge is fixed in a recess at the side of the edge, and has transversely directed back surfaces opposite the narrow sides of the metal cathode sheet.
At the edge protector provided by the present invention, there is form-locking between the metal cathode sheet and the profile strip, using a snap-fit connection that ensures firm form-locking of the two parts. The edge protector is easy to assemble and advantageous to install. Beyond that, it guarantees a great degree of imperviousness. Uncontrolled metallic efflorescences and prying apart of the edge protector are avoided. This leads to an improvement in equipment availability for the user. One can do completely without effortful and costly wax coating and decoating of the edge strips. A user""s repair cycles are also substantially lengthened, and thus repair and energy costs are decreased.
It is possible to convert existing metal cathode sheets, during repair work, by exchange or conversion of the edge protection system.
Another advantage of the invention is that, when pulling out the metal cathode sheets, drag-out losses of the electrolyte are very low because of the structure of the edge protector.
Counter-support surfaces can be provided that act together with the back surfaces of the holding wedges. This measure effectively supports the form-locking snap-fit connection between profile strip and holding wedge.
Holding elements can be formed at the narrow side of the metal cathode sheet. These support the vertical fixing of the edge protector and prevent slippage. Such holding elements can be formed, for example, by a slight material clinching at the narrow sides, using a blow of the hammer or crimping.
When there are several holding wedges arranged at a distance to one another, filler strips can be arranged between them. The filler strips are preferably formed as extension of the holding wedges at a head end. The filler strips fill the space between the holding wedges, so that the disadvantageous electrolyte drag-out losses during the pulling of the metal cathode sheets can be further reduced.
It is also possible to put a longitudinal groove into the holding wedges. The spaces between the individual holding wedges can be filled up with a suitable material via the longitudinal channels. Electrolyte-resistant plastic that can be cured or ceramic substances are available as such a material.
In another advantageous embodiment, the holding wedge and the edge protector are made of an electrolyte-resistant plastic, a metallic heat conductor being integrated into the holding wedge. This measure permits an additional contactless connection between the holding wedges and the profile strip. Using a suitable heat source, especially an inductive heating device, the material of the holding wedges and of the edge protector can be partially plasticized, using the metallic heat conductor, so that they weld together with each other. A further advantage of this embodiment is that the self-locking form lock can be additionally secured without adverse influence on the edge protector as such.